Depends, really.
It's true that the Ocarina of Time formula is starting to have a dejà vu feeling attached to it, but then again I'm not of those who complain when a sequel of a game is really close to the precedent game, I mean, if you want a all brand new gaming experience then you're better off not buying a sequel...
They might try to creat a whole new game system and use the Zelda brand for marketing reason. It might create some ruckus in the Zelda fan community if the game differs too much from the old formula, though. Especially if no other "classic" Zelda were to ever be produce.
In a perfect world, a completely new game would have an original background, story and characters, but given that the real world is far from perfect, often new game designs are using known IPs (Character/brand/background story) because of the market pull this IPs have.
Nintendo, amongst others, is known for that type of practice with game such as Mario Kart, Mario Golf, Mario Tennis, Mario Strikers, Mario Party, Mario Paint, etc... Which are all different games but have as a common point to use the Mario IP, which is a known brand in the videogame market.
Also worthy of note, some may argue that with the transition from 2D to 3D the canonical 2D formula of Zelda and Mario were changed, while remaining true to the original ideas behind the 2D gameplay.
Not to forget that the Zelda serie already had a few departure like Zelda 2, which was a 2D side scrolling adventure game, with random battles occuring on the overworld and most importantly RPG stats.
And how can we forget the Zelda CDi games?
Nah, I'm kidding, we can easily forget about thoses.